The central hypothesis of this application is that under physiological conditions, prolactin secretion from the anterior lobe of the pituitary gland is inhibited by dopamine and stimulated by oxytocin and that the activities of these neurons are regulated by clock genes, higher hypothalamic input and prolactin itself. This will be accomplished by pursuing 4 specific aims: (1) To characterize the role of OT neurons in control of PRL secretion under physiological conditions. To accomplish this, the incidence of FOS or FRAs staining of magnocellular and parvocellular OT neurons will be characterized during periods of physiologically induced PRL secretion. Antagonists of OT will be used to determine if endogenous OT controls PRL secretion under physiological circumstances. (2) To determine the nature of the afferent control of OT and DA neuronal activities under physiological conditions. This will be accomplished by first determining if there are VIP receptors on OT neurons and then administer antisense oligonucleotides to VIP (see Progress Report and Preliminary Data) and determine their effects on OT and DA neuronal activity as indicated by FOS or FRAs staining. (3) To determine if PRL feeds back on either OT neurons and/or their afferent controls to regulate their activities. First, it will be determined if OT neurons have PRL receptors and if so, immunoneutralize circulating PRL or administer ovine PRL and determine the effect on activity of these neurons. (4) To determine the molecular mechanisms controlling the circadian rhythm of neuroendocrine DA neurons involved in PRL secretion. The expression of clock genes and the phenotype of the neurons expressing them in the SCN, ARM or PeVN in a constant environment will first be characterized. Then, using antisense technology, their disruption will show function of the expressing neurons. The health relatedness of this project is to suggest new ways of treating diseases related to hyperprolactinemia and breast cancer.